Plastic bag



July 20, 1965 G. CAMERN 3,195,424

` PLASTIC BAG Original Filed May 25, 1961 4 Sheets-Sheet 1 July 20, 1965 G. cAMERlNl 3,195,424

PLASTIC BHG Original Filed May 23. 1961 y4 fShe'elbS-Sheeb ,-2

umn-"ft2" i T ooooooo l lguuul INV ENT OR. G/o/PG/O CAMSP/Nl.

July 20 1965 G. cA'MERrNl.: 33.195324 PLASTIC BAG Original Filed May 23. 1961 4 Sheecsq-She'ei'.- 4

INVENTOR Gf ops/o' CAME/20w.

ATTORNEY?,

United States Patent O 3,195,424 PLASTIC BAG Giorgio Camerini, Milan, Italy, assigner to Naim-Cellulosa, SpA., Milan, italy, a corporation of Italy @riginal appiication May 23, 1961, Ser. No. 111,971, now Patent No. 3,117,711, dated lan. 14, 1964. Divided and this application Sept., 3, 1963, Ser. No. 318,463 Claims priority, application Italy May 3i), 1960 6 Claims. (Ci. S13-35) This is a divisional application of a parent application Serial No. 111,971, filed May 23, 1961, now Patent No. 3,117,711 issued January 14, 1964 entitled Plastic Bag.

This invention relates to bags, and methods for making same, of types formed of plastic sheet material and more particularly to such bags adapted for use as shipping sacks and including among others, valve bags of such types adapted for the automatic packaging of granular and powdered materials.

Bags formed of plastic sheet material have heretofore been available and have generally been made by using a flattened tubular length of the plas-tic sheet material with the opposed wall edge portions at each end secured together by heat sealing, pasting or other means, such tube lengths being obtained by transversely cutting a continuous tube of the plastic sheet material. With such bags, one lcorner portion may be folded inwardly to provide a flap of a valve for permitting auto-matic filling of the bag, such valve flap being provided, if desired, with a sleeve or extension for facilitating closure of the valve.

Such conventional bags which are sometimes referred to as hat/ing a pinch bottom .type of closure, will assume an expanded pillow shape when filled and for this reason same cannot readily or securely be piled one on top of another in large numbers, inasmuch as they will tend easily to slide out of position. Furthermore, plastic bags having end closures such as above referred to, are not suficiently durable for heavy use inasmuch as the closure portions are not adequately reinforced and thus when same are subjected to heavy pressure or stresses in use, the end portions and valve regions may tear open or otherwise fail.

The present invention makes it possible to provide bags of plastic sheet material and particularly bags of a single walled valved type and which are free of defects such as above referred to.

In the manufacture of bags or shipping sacks of paper, it has been the com-mon practice to .provide end closures therefor in the form of side .and corner closure flaps which are folded into superposed relation and pasted in place, but so far as is known, it has not heretofore been appreciated that bags formed of plastic sheet material could have end closures satisfactorily formed of such flaps, and thas not been apparent how such flaps could satisfactorily be secured by heat sealing -or otherwise in such manner as lto provide a durable and eect-ively sift-proof end closure. But in `accordance with the present invention, a plastic bag, preferably of the single-wall valved type, is made possible, having end closures formed of superposed corner and side flaps and which are secured in place preferably by novel methods Iand arrangements of heat sealing so as to provide such bags with effectively reinforced and highly `durable end structures which will not become torn apar-t or permit leakage during heavy use. As a result, plastic bags, including valve bags, may be provided in accordance with the invention and which when filled will retain a generally parallclepiped shape convenient for handling, stacking and shipment and with the end closures so effectively reinforced that they will remain sealed even when the filled bags are subjected to heavy pressure.

Patented July 20, 1965 lCe Various further and more specific objects, features and advantages of the invention -will appear from the description given below, taken in connection with the accompanying drawings, illustrating by way of example preferred forms of the invention.

In the drawings:

FIG. 1 is a developed view of a .plastic bag blank in accordance `with lone embodiment of the invention;

FIG. 2 is a view of the same plastic bag blank in condition ready for formation of the end closures;

FIG. 3 is a further View of the same form of bag blank showing the con-dition of the closure liaps therefor during an intermediate stage in the manufacture of the bag;

FIG. 4 is a view of the nished bag while in flat empty condition;

FG 5 is a perspective view of the same embodiment of the invention;

FG. 6 is another view showing the positions and condition of various parts of the bag closures during intermediate stages in the manufacture of the bag and the heat Sealing of the end closures thereof;

FiGS. 7a .and 7b illustrate bottom or end closure portions of the bag during two alternative inter-mediate stages in the heat sealing thereof;

FIGS. 8 and 9 are views similar to FIGS. 2 and 3 but showing a somewhat different embodiment;

FIGS. 1() and l1 are `also views somewhat simil-ar to FfGS. 2 and 3 but illustrating a further embodiment;

FIGS. 12 and y13 are also similar views showing a still further embodiment; and

FiGS. 14, l5 and 16 are views similar to FIGS. l, 2 and 4 but showing yet another modification.

Referring now to FIGS. 1-4 inclusive in further detail, the plastic bag embodiment shown comprises a tubular body portion 2t) for-med of a length of plastic tubular sheet material such as of polystyrene or other and preferably readily heat-sealable plastic material. Such tubular plastic material may be formed by methods and means disclosed for example in UlS. Patents Nos. `2,461,975 and 2,844,846. As shown in the latter of said patents, such tubing may be provided along its sides with gusset formations so that if desired the bags formed thereof may have gussets along their sides, although the example of FIGS. 1-4 is ungusseted. It will be apparent also that the bags or bag blanks of these figures might be formed from flat non-tubular plastic sheet material, in which event lengths thereof would be folded over along a longitudinal fold line and the side edges heat sealed together to `form a tube.

As best shown in FIG. 3, the upper end closure for the plastic bag may be comprised of four closure flaps, viz. a side flap 21, which in the finished bag will be a side flap which underlies lan overlying side flap 22. Corner aps 23 and Z4 are provided which are folded inwardly of the bag to underlie both of the yside aps A2-1 and 22. In the usual case, in order to separate the side flaps from the corner flaps ofthe plastic tubing, the front wall of the bag blank, as shown in FIG. 2, i-s provided with slits as at 25, 26 exten-ding longitudinally of the bag tube, the rear wall as shown in `the developed View of FlG. l being also formed with corresponding slits 25a and 26a.

In shaping the end closure', the upper end of the bag blank, as shown in FlG. 2, may be folded forwardly about a fold line 27 and at that time the side flaps 21, 22 may be extended `to positions flatwise of the bag, as shown inl FIG..3, While the corner flaps 23, 24 become folded infolded over" into linalposition about so-called base fold linesas-indicatedat 30, 31,-in various of the gures. FIG.

4 shows the positions of the various iiaps after they'have'y of the base rfold lines,'that is theends ofthe slits terminate approximately at the side'edges of the cornerfflaps so that themarginal'side edgesofthe corner flaps are free'of slits.

In the form'shown in FIGS; 144, the profiling. of the lower end closureparts may be the same as'for those above described for the upper end closure and sameA are indicated fby the same referencenumbers on thedrawrngs, but accompanied by prime marks. However, asher'ein- Y the surface: ofthe side flap 21 thereunder.

after explained; one end closure or therother of the. bag,

upon bein'g sealed, will be leftwithza valve ,opening for example, at-the top, corner, or, 'if desired,` atv both top cor-V ners in case itis desired-to usethe bag with. filling machines having two lllingspouts for concurrently and morey rapidly fillin'grfthe bag, by material: introduced through bothtop corners.

After; thebag-end closures are'sealed and thebag is lled, it will assumera generallyrparallelepipedshape such'l aslindicated; in FIG. 5. Although along the corners or 4 turn having a row `of perforations v39 olfset with respect to those at 38V to provide the desired 'labyrinth seal.v

The preferred method and means for sealing the end closure flaps will now be described. First it is desirable to heat seal the marginal side` portions of the side flaps indicated at x in FIG. 3,0n the undersurfaces thereof, to

Ythe surface on theinside of `llaps 21 and 22 which contact therewith.Vv This may be accomplished` by placing the regions ofeachof Vthe base .foldlines 30 and 31' between the electrodes for example of a suitableknown form of dielectric heat sealinglapparatus. That is, one elongated electrode would be placed along beneath theregion of the lbase fold'li'ne as at 31 andthe other along the region on top of such line so Athatrthe plastic dielectric sheetv mate- 'rial therebetweenwill become heated and the contacting portions thereof thus sea-led together. Similarly, kelectrodes maybe applied along Lbase fold line'30 for/heat' sealing-the marginall portionsof `thecornerllaps there to In other Words, the,` side margins of the cornerv aps vwill be thus heat sealed to the side aps alongthose portions of the dottedrlinesindicated at 40 and 41.V Thus by these heat seals, the entirev end closure will be securely sealedexcept;

along that portionofnthe dot-ted lines indicated at 42, 43,

but-these portions as hereinafter explained will be covered' and sea-led when the side aps are folded overy and sealed. Also lthe Same heat ysealing electrodes as above'referred toWhen-applied may be utilized 'to serve the purpose of simultaneously applying heat marking lines to the, plastic. That is,.. the portions ofthe basefoldlines indicated at l 42 and 43 in FIG. 3 will be heat'rnarked so that, together edges. of each wall panel, the bagmaybe moreor less. rounded, yet the, main'or larger side wall surfaces. will be l f so nearly flat that numerous of the bags may be readily stackedv in position latwise. one upon another without liability of slipping out of place and without` causing undue pressure to be. applied tolth'e .contents in any region within the bag. While it will be apparent that the end closuresV of'the bagwhe'n initially sealed are flatwise of Y the bag when empty as shown in FIG. 4, yet afterthe bag.. y is filled the top and, bottom end' closure portions will as sume lpositions normal to the side'; Walls ofthe bag and furthermoregthese end closure regions willbe heavily re-V inforced because the greater part thereof'wifll be comprised of' at leastl two'thicknesses ofthe plastic sheet material. It is further noted thatl because of the fact that the marginaly side portions of the corner aps extend beyond the vbase fold lines, by the distances x as indicatedin FIG. 3,

the resultwill be that a greater part ofithe'corner lines as'at` 33, 34 will be exceptionally stronginthat same will be comprised of the thickness of portions of thel side. flaps plus the thickness of the marginal'portions indicatedvat x,A and furthermore as hereinafter explained, these portionswill be substantially integrally heat sealed together further contributing to the strengthdesirable at these reglons. Y

As further shown in FIGS. 3-5 inclusive, numerous small 'holesy or .perforations arer providedl to allow air to escape during. filling of they bag so that the bag will not become inflated, therebyeliminating all the troubles which might; otherwise occur due to the characteristic impermeability of the plastic sheet material of which the bag is formed; f These perforations, which are shown in the'draw-Y ings as somewhatexaggerated in size, are: preferably, so arranged' asto provide labyrinth seals at the regions'where sam'eoccur'. For example, on side ap 21,'a row-'ofp'erfol rations may be provided' as at,35 and on sideV flap 22' another rowV is provided at '36 along a line which, as'shown in FIG'.V4, will'be'offset with respect to the perforations` wlth'the lines of heat sealing at 4,0; 41, same will provide` defined .lines aboutwhich the sideltiaps 21, 22 areto'be. folded overpv-intofoverlapping-relation, and these defined. lineswill furtherV contribute to ,theforrnation of` defined shoulders for the Yend closure ofthe 1bag,'tendingto. cause.

same to assume itsde'sired box-like shape. Y

It,WilLbeunderstood that thelower closure end of: the

vbaginV FIG. 3 may be treatedandsealed in they same Y-rnanneri as-jabove described for the upper end closure.

In orderto complete the end closures, the side'iap21 is folded over and the side flap 2 2 isw folded over `insuper-l posedrelation to flap 21, and if Vfor example the valve4 isA to bellocatedy at corner flap 24, then theoverlying side flapsfmay be pasted ror otherwise secured' together land 4to the corner ilap 23 thereunder by bands or lines offad hesive located at the position indicated `by the dotted line 45` at the upper end ofY FIG. 4. And the side llap 22,1nay bey adhered tothe underlying side'flap,` 2-1' along aline or band as indicated by the dotted line 46.in FIG. 4; Similarly, atthe. bottom closureas shown, the overlapping side'flaps maybe adhered together by lines or. bands. of adhesive atf'the areas Yindicated by thev dotted lines 47, 48 and 49. At lines 47 and 48tl1esidel flaps; would not only be.. adhered together but also adhered to the corner aps thereunder if thereare to bel no valvesk at. this endclosure.

Incase theside flaps are to beadhered-by heat sealing, expedients mayy 'be followed as described below in connectionwithFIGS. 6, 7a and 7b. That is,'assumin'g that thetop end closure is to 'have a valve atl corner flap 24, thenaplate rnember50is placed overrthis corner flap as shown, and ini a position whereby its end will extend in. under corner flap l23,. This plate may bef-'a thermal insulation-plate,.in. ca se the heat sealing is Vto, be accomplished by theuse of heated bars or the like; or in' case ther-heating grounded. In either case, the plate will serve to prevent` the corner ap 23A from being heatl sealed to the bag pon 35fwhentlreaps are in closed condition. vTo further pro-k vifdefor venting ofthe bag during filling, if desired, a patch as'V at 371 may be applied' to the side wall of the bag and heat sealed thereto about its Vperiphery andservingptocow era row'of perfor-ations 38 in thebag wall', thepatch in" tionsthereunder at theti'me when heatsealing-is being acs complish'edV along lines such as at 45jand`4'6of FIG. 4.

o Incase ofheat sealing ofV the iside, aps, for example at the bottom'endzclosureof the bag 'where there is to be Vno valve, then theinner endportionsy as at V51, 52 of. the `corners 23",' 24 maybe folded Aover outwardly. This should be done before the marginal sides of the corner iiaps (as at x in FIG. 3) are sealed in place. Now as shown in FIG. 7b, plate members as at 5d, 55 may be positioned above the corner daps 23 and 24 respectively,

`these plates having their inner end portions positioned in under the folded over parts S1, 52, as shown. These plates being similar in function to the plate t), as above described, they will serve to insulate or protect the undersides of the corner flaps 23', 24 from being heat sealed to the bag portions thereunder at the time when heat sealing is accomplished (such as along lines d'7, 4S, 19, FIG. 4) for sealing the side flaps ZI, 22 together in superposed relation and to the folded-over portions 5I, 52 of the corner flaps. In this way, the end closure may be completely heat sealed and the several flaps heat sealed to each other along desired lines or bands, without danger of heat sealing the end closure portions of the bag to the underlying main wall portions of the plastic tube. In case an end closure such as in FIG, 7a is to be provided with valves at each corner, then the corner -flaps may both be provided with folded over portions as at 51, S2 and a plate as at 56 may be provided to extend entirely across the end closure above the corner iiaps so that thereafter the side ilaps 21, 22 may be fol-ded over in superposed relationship and heat sealed to each other without heat sealing same to the corner iiap portions thereunder, thereby leaving valve openings beneath the ends of the superposed corner flaps.

Under certain circumstances, it may also be possible to insulate various of the layers against becoming heat sealed together where not desired, by covering same with powders such as talcum, asbestos or the like.

Another form of the invention shown in FIGS. 8 and 9 is similar to that above described in connection with FIGS. 16, 7a and 7b, except that the construction of FIGS. 8 and 9 differs in that the slits as at dii, el extend far enough to meet the base fold line 62 so that, as is apparent from FIG. 9, the corner iiaps 63, ed will not have any side marginal portions such as at x, as described above in connection with FIG. 3. Yet the side flaps as at 65, 66 may be folded over in superposed relation and sealed in a manner similar to the sealing of the side flaps of the embodiment previously described. In this embodiment, the heat marking lines, such as above described, may advantageously be formed to extend throughout the length of the base fold lines 62.

In a further embodiment of the invention, as shown in FIGS. l0 and 11, a bag blank is so profiled in forming same that the side aps such as at 7i), 7l of each end closure when folded into closing position, overlap by only a relatively narrow area, as indicated at y in FIG. 11. This may be accomplished by cutting the ends of the bag tube with a three-step profile, as shown in FIG. 10. That is, the mid-portions which are to form the side flaps are cut to an intermediate length, whereas portion 72, which is to form one of the corner flaps, is cut with an abbreviated length and the portion '73 which is to form the opposite corner iiap is cut to a more extended length. The portions at the other end closure as at 7d', '72', 73 are so cut as to be complementary to the upper end of the bag so that succeeding tube lengths may be cut from continuous tubing without waste of material.

As indicated at the bottom end closure of FIG. 11, the side flaps may be sealed to each other and to the corner aps thereunder along lines or bands such as indicated by the dotted lines .74, '75 and 76 in a manner corresponding to the way in which the bottom closure of FIG. 4 is sealed along lines 47, 48 and 49. In other respects, the end closures of FIG. 1l may be closed and sealed in a manner similar to that above described in connection with FIG. 4.

FIGS. 12 and 13 illustrate an alternative way for forming a construction similar to that of FIGS. and 11. Here the corner flaps 80, 31, Sil and SI may be like the corner aps of the construction of FIGS. 10 and 11. However the side flaps 82 and 83 are of dierent lengths which d are complementary respectively to the side flaps 32 and 83 at the bottom closure. As in the case of FIGS. 4 and 11, the side aps may be adhered or heat sealed to each other and to the corner flaps beneath same where necessary along lines in under the dash lines indicated at 84, S5 and Se in FIG. 13.

We will refer now to the further embodiment of the invention shown in FIGS. 14, l5 and 16 which differs principally from those previously described in that heat sealing of the upper and lower edge portions may be carried out on the bag element before folding the flaps. In this case, it is possible to seal the edges without using any means of lirnting the heat sealing only to the layers to be heat sealed. FIG. 14 is a view showing the developed profile of the whole bag element, the ends of which may be cut straight across and the outline of which is indicated by the numerals 9i, 92, 93, 94. The edge 91- 94 is of course intended to be joined to or made integral with the edge 92-93 when the front and back portions of the bag are folded about the dotted line 95-96 as in FIG. l5. The upper edge of the blank is formed with slits as at 97, 9S which demark the sides of the corner flap at the valve corner in the finished bag, these slits preferably extending so as to each be of a length about equal to half of the width of the end closure of the completed bag. An extension piece may be advantageously adhered or otherwise secured to the upper end of the valve corner iiap 99, as shown in FIG. 14.

The blank may be formed with various crease lines as shown by the dotted lines in FIGS. 14 and 15, these, if desired, being heat mark lines made as above explained in reference to heat marking lines of FIG. 3, these lines demarking the fold lines for forming the end closure portions including the diagonal lines demarking the corner aps.

When the unit is in the condition shown in FIG. 15, the front and rear opposed upper edges may be heat sealed together straight across the unit, except at the portions forming the valve corner flap. Similarly the opposed front and back edges of the blank at the bottom may be heat sealed together. After that is done, it will be found possible to fold the top and bottom end closures in such manner that they will assume the apperance shown in FIG. 16. That is, all of the corners, except the valve corner, will be found to have what will be in effect similar to corner flaps as at ISI, ItiZ, 193 and there will be formed integrally with each, triangular free tab portions as at Idd, M35 and 06. These triangular tab portions will more or less protrude from the remaining portions of the end closures of the bag and thus same may be used for readily grasping and better handling of the bag. However, if desired, these triangular portions may be cut off after heat sealing the flap portions forming same along lines such as indicated by the dotted lines 197.

What is claimed and desired to be secured by Letters Patent is:

l. A method of making a sift proof bag from a single walled tube of plastic material, said method comprising the steps of folding outwardly and away from each other about side iiap lines, oppositely disposed portions of one end of said tube, folding the remaining oppositely disposed portions of said one end of said tube inwardly toward each other so that the side marginal interior surfaces of said other portions overlay correspondingly facing interior surfaces of each of said rst mentioned portions along said side flap lines, applying heat along at least one of said side flap lines to seal said interior surfaces, folding over said iirst mentioned portions along said side ap lines inwardly toward each other in overlapping relationship and adhering them to each other.

2. A method of making a sift proof bag from a single walled tube of plastic material, said method comprising the steps of folding oppositely disposed side flap portions of one end of said tube outwardly and away from each other about side flap lines, subsequently folding inwardly towardA eaehV otherv theV Vremaining corner apl portions of said one end of ksaid tube so that Vthe side 'marginal' interior surfaces of said corner 'apfportionsroverlay correspondingly facingdnterior surfacesof` each of said side flap portions alongJv saidA side flap lines, applying heat along the entire length of each of said side flap linesl to seal said interior surfaces and to generate fold creases thereby, folding said side flapV portions about sai-d'fold` creases inwardly toward each other in overlappingrela-V tionship and adhesively adhering said side flap portions to said corner ap portions and to each other in their overlapping relationship. K

3. A method of making a sift proof bag from a single walled tube of plastic materiaLjsaid method comprising the steps of slitting saidtube longitudinallyrat one end tofform twooppositely disposed corner aps interspersed between two oppositely disposed side ilaps, first folding said side flapsoutwardly away from each other along walled tube of plastic material, said method comprising" the steps of slitting said tube longitudinally at two places on one end to form two opprositely'disposed corner. flaps interspersed between two oppositely disposed side flaps,

rst folding said side liaps outwardly away from each-y other along sideV flap lines,` subsequently folding ysaid corner flaps inwardly toward eachother `so `that the side marginal interior surfaces of said Ycorner flaps overlay correspondingly facing interior surfaces of each ofl said element from under said heat sealed overlappedside Y flaps, placingva second heat insulative elementwhichextends between said Vside flap lines over .saidone corner; ilap and under its folded bacioinnermostY extremity and applyingheat with said second heatinsulative element in' place to seal the overlapped sidejiaps to sjaid folded back innermost extremity of said-one corner flap; l'

5. A method of making asift'proofba'gffromv av single;

walled tube of' plastic material, saidlmethod comprising the steps'of folding koppositely disposed sidey flapvportions of one'end of saidtube outwardlyl and' away from each other about side ap lines, and subsequentlyV foldinginf. wardlyftoward each other the remainingfcornerap `por-' tions of saidone end of saidtubeso that 'the side mar.-v ginal interiork surfaces of saidcorner flap portions overlay correspondinglyV facing interior s urfacesjofl eachi of said side flap-portions alongsaid side flap; lines, covering the.

. region between said sidefla-p lines with ajheatfinsulative.

element,applying-beata along the exposedfportions of said tube to seal saidinteriorl surfaces, folding said;sideaps along said side ap'lines inwardly-toward'eachiotherin overlapping relationship and heat sealing; said side flaps v to each other and to said corner flapsin suchl arrange-y side aps along said side flap. lines, further folding thel innermost extremity of atleast one of said corner flaps between the longitudinal slits thereof, back away from the other corner flap, applying heat along the length of each of said side flap lines to seal the various facing surfaces along said side ap lines, placing a first heat insulative element which extends betweeny said side flap lines over both said corner flaps includingy the innermost extremites thereof', folding said side iiaps along said sid-e flap lines inwardly toward each other in overlapping relationship and over said first heat insulative element, applying( heaty with said first heat insulative element in place to seal said side aps to each other, removing saidy first heat insulative Y ment. i f

6. A method of making a'sift` proof: valve bagfrorn` a single walled tube Vof plastic materiaL'said methodt comprising the steps of slitting said tube longitudinally at one end to form two oppositely disposed corner flaps: interspersed between two oppositely disposed; side flaps,

, first folding said side flapsV outwardly; away from each other along rsideY flaplines and thenl foldingjsaid, corner flaps inwardly toward eachother so that thesidemarginal interiorvsurfaces of said corner; flaps overlay correspondingly facing interiorsurfaces VofV each of'said side' `flaps along saidsideflap lines; covering the region betweengsaidvl side flap lines with a heat insulativeelement which, veX- Vtends overfone corner apand underkthefother corner.;

flap, applyingjheat toV sealV saidhinteriorY surfaces,r,furtherr folding; ,said side flaps inwardlyl about said side' ap lineslinto overlapping,relationshipand applying heat with1 said heat insulative element in place to seal said. side .flaps'toeach other and` tofsaid one corneriap;v f

References Cited by the Examiner FRANK E; BAILEY, Primary Examiner. 

2. A METHOD OF MAKING A SIFT PROOF BAG FROM A SINGLE WALLED TUBE OF PLASTIC MATERIAL, SAID METHOD COMPRISING THE STEPS OF FOLDING OPPOSITELY DISPOSED SIDE FLAP PORTIONS OF ONE END OF SAID TUBE OUTWARDLY AND AWAY FROM EACH OTHER ABOUT SIDE FLAP LINES, SUBSEQUENTLY FOLDING INWARDLY TOWARD EACH OTHER THE REAMINING CORNER FLAP PORTIONS OF SAID ONE END OF SAID TUBE SO THAT THE SIDE MARGINAL INTERIOR SURFACES OF SAID CORNER FLAP PORTIONS OVERLAY CORRESPONDINGLY FACING INTERIOR SURFACES OF EACH OF SAID SIDE FLAP PORTIONS ALONG SAID SIDE FLAP LINES, APPLYING HEAT ALONG THE ENTIRE LENGTH OF EACH OF SAID SIDE FLAP LINES TO SEAL SAID INTERIOR SURFACES AND TO GENERATE FOLD CREASES THEREBY, FOLDING SAID SIDE FLAP PORTIONS ABOUT SAID FOLD CREASES INWARDLY TOWARD EACH OTHER IN OVERLAPPING RELATIONSHIP AND ADHESIVELY ADHERING SAID SIDE FLAP PORTIONS TO SAID CORNER FLAP PORTIONS AND TO EACH OTHER IN THEIR OVERLAPPING RELATIONSHIP. 